Hampus Olsson, who designed the wallpapers for OnePlus, shared high-resolution versions of them on his personal blog. If you go to the source link below, he provides a .zip file that includes all of them in both 1080p and 4K resolutions.

They're all designed for the 5T's 18:9 display, so they're perfect for other tall phones like the S8, Note8, and Pixel 2 XL. I definitely think Olsson did a great job with these backgrounds, and I'll probably be using a few of them on my Pixel.